Portable triboelectric-electromagnetic hybrid biomechanical energy harvester for driving various functional light-emitting diodes with a wide range of wavelengths

As the application range of light-emitting diode (LED) has rapidly expanded in various fields and functional LED-implanted electronic devices have deeply permeated human daily lives, research on the electrically off-grid power supply method for LEDs is being widely conducted around the world in order to further strengthen and utilize the strong points of LEDs. In this study, a shaft-shared triboelectric-electromagnetic hybrid portable energy harvester (STEP) considering the electromotive force-based hybridization is proposed to drive various functional LEDs with a wide range of wavelengths using biomechanical energy. The respective roles and functionalities of triboelectric nanogenerator (TENG) and electromagnetic generator (EMG) in a hybrid energy harvester are experimentally and visually demonstrated by comparative investigation in parallel and series circuits. Then, based on the experimental result, the necessity of hybridization of TENG and EMG is described from the perspective of both electromotive force and current for the LED-involved devices. When the STEP operation speed is 500 rpm, the average output voltage and current of the TENG and EMG parts are experimentally characterized, and the average output voltage from TENG is 238 V and the average output current from EMG is 18 mA. The maximum peak powers of TENG and EMG are 1.92 and 26.7 mW when the external load resistances are 30 MΩ and 400 Ω, respectively. STEP is portable in size and weight, and it can be operated by human force thanks to an optimally designed gearbox. When STEP is driven by human power, it can power a variety of functional LEDs ranging from 275 to 850 nm of wavelengths, including 250 visible, 50 infrared, and dozens of UV LEDs. Given that the superior functionalities of LEDs have been validated, and that the synergistic effect through convergence with electrical grid-independent power supply technology is thought to have great potential in a variety of fields, STEP is expected to serve as a guideline for effective energy supply strategy to various functional LEDs in related fields such as lighting, engineering, security, and healthcare industries.